Nutrients supplied by connective tissue below the epithelium
Basement membrane
Thick band under the basal region of the epithelium
Basement membrane is a light microscope term
Basal lamina is an electron microscope term (on EM level, basement membrane has 3 layers)
Part of connective tissue
Polar
Apical surface contains cilia; basolateral does not, etc.
Cellular junctions
Dark band below cilia is the terminal bar where junctional complex resides
Zonula occludens, zonula adherins, and macula adherins
Zonula occludens form a tight junction, blocking passage of materials and forcing them to cross through epithelial cells rather than around them
Terminal web is nearly the same place, where cilia microtubule axoneme attaches
Free surface
Highly cellular, forming a sheet
Jejunum
Surface modifications:
Brush-border composed of microvilli
Microvilli on apical surface forming a continuous band called the brush-border
Microvilli too small to see individually on light level
Function of microvilli
Increased surface area for absorption
Goblet cell
Located in G.I. tracts, found in epithelial tissue
Unicellular mucus gland
Terminal Web
Located underneath the apical membrane
Core actin filaments of microvilli are attach to terminal web
Epithelium
Elongated simple columnar cells
Epididymis
Surface modification:
Stereocilia
Diagnositic characteristics: longer than microvilli and can be seen in clumps
Length of stereocilia up to 20-25% length of cell
Not motile
Structure
Actin filament core
Epithelium
Pseudostratified columnar
Trachea & Esophagus
Surface modification:
Cilia
Diagnostic characteristic: Taller and denser than brush border microvilli but shorter than stereocilia
Individual striations visible
Function
Motile – moving mucus along surface
Beat in synchronization – coordinate beating between cells by gap junctions
Gap junctions composed of connexons made of connexins
Not visible on light microscope level
Gap junctions are all over the basalateral component of epithelium in addition to being in the terminal bar
Epithelium
Pseudostratified ciliated columnar
Diagnostic characteristics: layered nuclei but columnar cell
Cells not seen one on top of another
All cells sit on basement membrane
Cells in connective tissue
Could be fibroblasts, macrophages, lymphocytes
Asthmatic patient
May have influx of immune system cells
Spermatozoa
Flagella
Composed of microtubules in an axoneme
Longer than cilia and only one per cell
Moves the whole cell
Has a mitochondria wrapped around it
Artery, Vein, and Nerves
Nerves
Packed full of neurons, no lumen
Artery
Has a lumen with thick layer of muscle cells
Inside layer of smooth muscle cells is the internal elastic lamina
Epithelium
Simple squamous
Very thin to allow passage of nutrients and waste through the epithelium
Nucleus is typically a squished disk
On the lumen of the vessel
All blood and lymph vessels in body are simple squamous
Vein
Larger more irregular lumen
Thyroid
Made up of follicles – hollow spheres
Have a wall of simple, cuboidal epithelium
Round nuclei, cell is long as it is tall, single cells
Free space is the hollow sphere so basement membrane is on the other side of the epithelium
Kind of like swiss cheese the hollow areas where the apical surface is
G.I. Tract
Epithelium
Simple columnar – Tall narrow cells in one layer
Brush-border on apical surface
Be aware of planar artifacts
In some portions, it appears to be pseudostratified because the section is cutting through different layers of cells
However, further downstream, most cells look more simple columnar, indicating the correct epithelial type, and suggesting that the pseudstratified look in upstream cells is in reality a planar artifact
Skin
Epithelium
Keratinized stratified squamous
Cell on surface lack nuclei because they are so full of keratin that the cells have died
Five layers – that you don’t have to know
Stratum Basale
Germinal layer that produces new skin cells, pushing cells towards the surface
Cells differentiate on the way to the surface
Stratum Spinosum
Straum Granulosum
Stratum Lucidum
Stratum Corneum
Esophagus
Epithelium
Non-keratinized stratified squamous
Nuclei of cells reaches the apical surface, so they are non-keratinized
Urinary Bladder
Non-Distended Epithelium
Translational epithelium or uroepithelium
Diagnostic characteristics: Look at surface cells for shape, and determine if they extend over several layers of cells.
Translational epithelium looks like stratified with lots of nuclear layers with cuboidal surface cells but cells aren’t the same size the whole way down and extend over several layers of underlying cells
Stratified epithelium has cells all the same size and don’t overlap
Distended Epithelium
Epithelium is stretched out with maybe 3-5 layers on surface
Appear to be squamous cells now, but still overlap several cells under it
Glands
Classified structurally, mode of secretion, secretion type, presence/absence of ducts
On high magnification, mucus cells are lighter staining because the mucus gets sucked out of cells during preparation, leaving a light lacy apparent of cytoplasm in mucus cells
Serous cells secrete serous secretions very quickly and don’t get left in the cell, leaving only the machinery (ribosomes, etc.) behind
If both cells are present, then it’s a mixed gland
Epithelium of duct is simple high cuboidal or low columnar
Microanatomy Lab – Epithelial Tissues Lab
Dr. Robert Crissman, Ph.D.
Table of Contents
Epithelium
Jejunum
Epididymis
Trachea & Esophagus
Spermatozoa
Artery, Vein, and Nerves
Thyroid
G.I. Tract
Skin
Esophagus
Urinary Bladder
Glands
Axillary Skin
Salivary Gland